1. Field of the Invention
The present invention concerns a shut-off valve having a double seat.
2. Description of the Prior Art
Double-seat valves are known for example from DE 31 46 590 and EP 0 645 562. DE 31 46 590 describes double-seat valves in which the inside diameters of the valve seats differ by a relatively great amount. As a result, when a pressure obtains between the valve heads, the opening force of the upper valve head which is of a larger inside diameter is greater than the closing force at the lower valve head.
Specifically for use as automatic shut-off valves for gas burners and gas appliances, the standard which applies in relation thereto is DIN EN 161 which establishes test criteria for approval for such valves. In regard to the definition of the classes of valves, it takes account of the double-seat valve in that the standard concerns a valve in class A, B or C if the sealing force is not reduced by the action of the intake pressure of the gas. By virtue of that definition, there are valves in the same class, with a differing shut-off characteristic in relation to a rising intake pressure. If a disc-type valve, for example in class B, can be subjected to the action of pressure until any component involved in the test fails, then in the case of double-seat valves in accordance with the standard, sealing integrity is no longer demanded after the maximum test pressure specific to the valve is exceeded. The reason for this is that the sealing force is essentially produced by the closing spring force and a component which assists the closing force, arising out of a possible differential area between large and small seat diameters, cannot be converted to the same extent into a rise in shut-off pressure against both seats, in the known structures. Added to that is the fact that the force which obtains at the differential area has to be overcome, when opening the valve. Specifically in the case of solenoid actuating units therefore the differential area is kept as small as possible, which minimises the proportion of the dynamic pressing force in terms of the static spring biasing force.
Besides the purely static pressure loadings, valves are also exposed to dynamic pressures which arise upon closure of the valves and which occur in particular at relatively high flow speeds and which can exceed 1.5 times the maximum operating pressure. A valve is also exposed to higher intake pressures if an upstream-connected high-pressure regulator exceeds its set outlet pressure.
The object of the present invention is to provide a shut-off valve having a double seat, which effectively prevents gas from passing through the shut-off valve, up to the specified bursting pressure of the valve.
In accordance with the invention, there is provided a shut-off valve having a double seat with an upper valve seat of a diameter D1 and a lower valve seat of a diameter D2 different to the diameter D1 (D1 less than D2), and a double-head setting member which in the closed condition prevents passage therethrough of a medium which is to be sealed off, wherein the annular surface (D2xe2x88x92D1) of the double-head setting member, which is acted upon by the medium to be sealed off and affords a closing force, and is formed from the outside diameter D2 and the inside diameter D1, is divided by a diameter D3 (D1 less than D3 less than D2) into at least two regions in order to distribute the closing force to the upper valve seat and the lower valve seat.
Therefore the core of the invention is that there is provided a defined differential area as an operative surface for the intake pressure, which is divided into sections which are resiliently and pressure-tightly connected together and directly or indirectly transmit the respective sealing force components to the large or small valve seat diameter respectively, wherein the closing spring forces which must satisfy the counter-pressure test in accordance with DIN EN 161 act separately on both seats and thus produce the initial shut-off pressure.
In comparison with single-head valves, double-seat valves admittedly suffer from the disadvantage of requiring more individual parts and a higher level of production accuracy, but in regard to the opening energy to be applied and the required volume for installation of the valve, they have major advantages, in comparison with single-head valves with the same through-flow, in terms of lower weight and a lower level of power consumption, for which reasons this type of valve will also assert itself in the future. The mean seat diameter in the case of the double-seat valve is only 70% of the seat diameter in the case of the single-seat valve and also the stroke movement which is so important for optimisation of solenoid drive units is also reduced to 70% in the double-head valve.
Due to the force equalisation effect arising out of the oppositely disposed surfaces which are subjected to the action of pressure, which forms the basis for the design configuration of the double-head valve, the pressure-loaded surface which is relevant for the opening pressure is reduced, in comparison with the single-head valve, to a circular ring as the difference between the large and small seat surfaces, whereby large reductions in regard to the opening forces are achieved, particularly in the case of valves with a relatively high admissible operating pressure and relatively large nominal widths.
Further advantageous configurations of the invention are set forth in the dependent claims.